This invention relates generally to soldering of electronic components onto a printed circuit board, and more particularly to a soldering method of a printed circuit board having mounted thereto high density electronic components with narrow lead gaps.
When electronic components are soldered to a printed circuit board, excessive solder and solder bridge become serious problems particularly in high density electronic components. The following two methods have been known in the past as the methods of removing the excessive solder and solder bridge that occur when soldering. The first method directly puts a soldering iron to a solder portion and absorbs any unnecessary solder, and the second method absorbs the unnecessary solder by capillary action using a twisted copper wire impregnated with a specific flux (such as "Solder Wick", a product of C.S.C. Co., Ltd.).
Since the conventional methods described above are in a sense the countermeasures for the excessive solder and the solder bride that have already been formed, they do not naturally contemplate at all how to prevent the formation itself of the excessive solder and the solder bridge, and are not free from the following problems.
(a) When the solder is built up excessively on the twisted wire, the wire does not absorb the solder any more and hence, must be discarded.
(b) Whether or not soldering has been made satisfactorily must be confirmed with the eye when using a soldering iron or a solder absorbing wire. Accordingly, if the soldering iron or the wire is put to the solder portion that has been made completely, the solder at that portion will become insufficient.
(c) An apparatus for automatically checking the soldered state is so expensive that an apparatus for automatically absorbing and removing the excessive solder becomes expensive as a whole.